<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .fa{
            width: 400px;
            height: 1600px;
            border: 1px solid red;
            /* 相对定位 */
            position: relative;
            /* 去掉多余部分 */
            overflow: hidden;
        }
        .box1,.box{
            width: 200px;
            height: 200px;
            background-color: cyan;
        }
        .box2{
            width: 200px;
            height: 200px;
            background-color: darkcyan;
            /* 绝对定位 */
            position:absolute;
            left:10%;
            top: 100px;
            /* 层级改低一点  负数在最下层  正数在上边*/
            z-index: -1;
        }
        .box3{
            width: 100px;
            height: 100px;
            background-color: salmon;
            /* 固定定位 */
            position: fixed;
            left: 500px;
            top: 500px;
        }
    </style>
</head>
<body>
    <div class="fa">
    <div class="box1"></div>
    <div class="box2"></div>
    <div class="box"></div>
  </div>
   <div class="box3"></div>
    
</body>
</html>